Natural rubber, cis-1,4 polyisoprene, a biobased elastomer, is produced primarily in tropical climates by the Brazilian rubber tree, Hevea brasiliensis (Hevea). Natural rubber is essential in many industrial applications and in many of its most significant applications, natural rubber cannot be replaced by synthetic alternatives. Because of its desirable properties and heavy demand, the price of natural rubber is rising, making natural rubber increasingly more precious as an industrial material. Indeed, in 2011, 10 million MT of natural rubber (NR) valued over $10B USD was harvested for use in commerce.
Unfortunately, users of natural rubber not only face rising prices, but also the potential for shortage. Indeed, the demand for Hevea rubber is expected to exceed supply by 25% by 2020.
Natural rubber is unique in that for many applications it has no synthetic equivalent. Indeed, its unique properties of resilience, elasticity, abrasion- and impact-resistance, efficient heat dispersion, and malleability at cold temperatures are unmatched by synthetic alternatives (see e.g., Cornish (2001) Phytochemistry 57, 1123-1134). For example airplanes cannot safely land with tires made from synthetic rubber; and only truck tires made from natural rubber are resilient enough to withstand heavy shear and loads. Thus, potential shortages of natural rubber foretell profound consequences for commerce.
Unfortunately, today, Hevea brasiliensis is essentially the sole commercial source of natural rubber. But, fortunately, there are alternative plant sources for natural rubber. Chief among the alternatives is guayule (Parthenium argentatum Gray). Parthenium argentatum Gray commonly known as guayule, is a shrub in the family Asteraceae, native to the southwestern United States and northern Mexico.
On its own, guayule is presently not economical without either greater rubber yields or identification and development of high value coproducts. However, if developed, guayule has great potential as a new or alternative crop for arid and semiarid areas of the southwestern United States, north central Mexico, and regions with similar climates around the world (see e.g., Thompson and Ray 1989; Wright et al. (1991) Guayule economics, p. 351-366. In: J. W. Whitworth and E. E. Whitehead (eds.). Guayule natural rubber. Office of Arid Lands, Univ. of Arizona, Tucson). Thus, development of guayule cultivars capable of producing high yields of natural rubber latex would be invaluable for increasing the quantities of natural latex rubber.
Therefore, what is needed in the art, are methods for improving the quantity and/or quality of natural rubber from guayule, and new guayule cultivars capable of producing high yields of natural rubber latex.
Fortunately, as will be clear from the following disclosure, the present invention provides for these and other needs.